1. Technical Field
The present disclosure relates to a toner, a developer, an image forming apparatus, and an image forming method.
2. Description of Related Art
In an electrophotographic image forming apparatus or electrostatic recording device, an electric or magnetic latent image is developed into a toner image. In electrophotography, for example, an electrostatic latent image is formed on a photoreceptor and is developed into a toner image. The toner image is transferred onto a recording medium, such as paper, and fixed thereon by application of heat, etc.
It requires a large amount of electric power for melting and fixing the toner image on the recording medium. Therefore, toner is required to be fixable at much lower temperatures (this property is hereinafter referred to as “low-temperature fixability”) from the viewpoint of energy saving. Toner is also required to be easily releasable from a heating member, such as a fixing roller, so as not to cause hot offset (this property is hereinafter referred to as “hot offset resistance”).
One proposed method of improving hot offset resistance involves including a release agent in toner. (Such a toner may be referred to as an oilless toner.) As the release agent, natural waxes such as carnauba wax (i.e., plant) and paraffin wax (i.e., crude oil), and synthetic waxes such as polyethylene wax and polypropylene wax have been used for toner. However, these release agents not always sufficiently improve hot offset resistance of toner.
As an attempt to improve hot offset resistance, Japanese Patent Application Publication No. 2009-092927 proposes a release agent comprising an ester of a polyglycerin having an average polymerization degree of 2 to 10 with a fatty acid having an average carbon number of 16 to 24.
Low-temperature fixability of toner may be also improved by controlling thermal properties of binder resin. As an attempt to improve low-temperature fixability, Japanese Patent Application Publication Nos. 2008-262179 and 2010-014757 each propose a toner including an amorphous polyester resin, the main chain of which having a polyhydroxycarboxylic acid skeleton comprising L-monomer and D-monomer at a specific ratio (e.g., polylactic acid).